The present invention relates to a system for blending a supplementary brake with a primary brake such as to provide total braking in accordance with a certain chosen brake command.
On railway vehicles, for example, particularly electric locomotives and self-propelled railway transit cars, the traction motors may be operated as electric generators during braking in order to dissipate the dynamic energy of the vehicle in the form of heat via the dynamic braking grids of the vehicle. Since the traction motors are already available for propelling the vehicle during a propulsion mode of operation, this form of braking, commonly referred to as dynamic braking, represents a low-cost means of retarding the vehicle. Unfortunately, however, the slow response upon initiation of braking and a fade characteristic when approaching a stop dictates the use of an additional brake, in particular a friction brake, as a means of making up for any deficiency in the dynamic brake effort attained. As a complement to the dynamic brake, therefore, a friction brake is traditionally employed to assure that the proper brake effort is realized.
Justification for the additional expense brought about by the requirement of a supplemental friction brake when using dynamic braking is the fact that modern rail passenger transportation demands higher speed, safer operation, closer spaced stations, and programmed speed control, all of which add emphasis to the need for a coordinated multi-brake system.